1. Field of the Invention
The present invention relates to a yoke for a voice coil motor, defining a gap in which a voice coil is disposed, and introducing a magnetic flux from a magnet to the gap so as to drive the voice coil in response to an electric current flowing through the voice coil.
A voice coil motor including the above-mentioned yoke is in particular applied to an information recording apparatus for driving a recording and/or reproducing head along an information recording medium in accordance with the movement of the voice coil. The information recording apparatus may be represented by a magnetic disk drive unit, and so on.
2. Description of the Prior Art
Reduction in size and weight is required in a portable information processing terminal such as a personal computer of notebook type. Accordingly, the requirement to reduce the size of a file unit or magnetic disk drive unit, which is installed in a portable information processing terminal of small size, is becoming severer.
For example, Japanese Patent Laid-open publication No. 4-345974 discloses one method to reduce the thickness of a magnetic disk drive unit. The method provides a yoke for a voice coil motor unified with a housing of the magnetic disk drive unit. The same idea can also be observed from Japanese Patent Laid-open publication No. 5-41044, FIG. 5, and Japanese Patent Laid-open publication No. 6-236660.
The performance of an actuator depends upon the intensity or density of magnetic flux in the gap. The density of magnetic flux can be improved by increasing magnetic force from the magnet, or by increasing saturation flux density in the yoke. As the density of magnetic flux increases, the acceleration performance of an actuator can be improved. On the other hand, if adequate acceleration performance is already realized, the size and thickness of the magnet may be reduced.
In a given case where a gap is defined by upper and lower yokes, for example, the density of magnetic flux can be improved by providing a side yoke for connecting the upper and lower yokes so as to reliably circulate lines of the magnetic flux. However, techniques disclosed in the above-mentioned publications fail to consider the advantages of the side yoke.
The object of the present invention is accordingly to provide a yoke for a voice coil motor capable of increasing the density of a magnetic flux by reliably circulating a magnetic flux through a side yoke, so as to contribute to further reduction in size and thickness of an information recording apparatus such as a magnetic disk drive unit. Another object of the present invention is to provide an information recording apparatus and a cover thereof capable of reducing the number of parts and the assembling and production cost.
According to a first aspect of the present invention, there is provided an information recording apparatus comprising: a head; a carriage carrying the head; a housing body supporting the carriage; a cover made of a magnetic plate forming a side yoke; a lower yoke magnetically connected to the cover through the side yoke; a magnet mounted on at least one of the cover and lower yoke; and a coil mounted on the carriage and disposed between the cover and lower yoke.
According to a second aspect of the present invention, there is provided a cover made of a magnetic plate for an information recording apparatus, forming a upper yoke opposed to a lower yoke provided in a housing body when the cover closes the housing body, and a side yoke connecting the upper and lower yokes within the housing body when the cover closes the housing body.
The housing body may enclose a recording and/or reproducing head capable of recording and/or reproducing information data from and/or to an information recording medium. The cover may close an opening defined in the housing body. The lower yoke may be opposed to the cover so as to define a gap between the cover and itself. Magnetic flux generated from the magnet flows through the cover and lower and side yokes. When an electric current is supplied to the coil, the coil moves in response to the supplied electric current based on the magnetic flux introduced to the gap. The movement of the coil is transmitted to the head by means of the carriage. The integral formation of the side yoke to the cover contributes to reduction in the number of parts, and to a facilitated assembling and manufacturing leading to reduction in production cost. Moreover, connections between parts in the yoke are reduced so that the loss of the magnetic flux flowing through the yoke can be restrained to the utmost. This may allow reduction in size and thickness of the magnet. In particular, if the magnetic plate is processed by a press for forming the cover and side yoke, it is possible to reduce the cost for making a mold.
In addition, the cover may also form the lower yoke in the information recording apparatus. This may contribute to further reduction in connections between parts in the yoke. The loss of the magnetic flux in the yoke may further be reduced. In particular, if the magnetic plate is processed by a press for forming the cover and side and lower yokes, it is possible to reduce the cost for making a mold.
A gap adjustment protrusion may be embossed on the cover by a press. The protrusion may serve to adjust an extent of the gap between the upper and lower yokes in the information recording apparatus. The adjustment of the extent of the gap enables control for the density or intensity of the magnetic flux generated in the gap.
A positioning protrusion may be embossed by the press for positioning the magnet. Otherwise, a positioning recess may be formed by etching on the cover for positioning the magnet in place of the positioning protrusion. In either cases, positioning the magnet serves to allow the magnetic flux from the magnet to reliably circulate in the yoke for voice coil motor.
According to a third aspect of the present invention, there is provided an information recording apparatus comprising: a head; a carriage carrying the head; a housing body made of magnetic material and supporting the carriage; a cover made of a magnetic plate forming a side yoke; the side yoke magnetically connected to a bottom of the housing body; a magnet mounted on at least one of the cover and the bottom of the housing body; and a coil mounted on the carriage and disposed between the cover and the bottom of the housing body.
With the arrangement of the third aspect, the cover and housing body serving also as the upper and lower yoke for defining the gap enables, in addition to the advantages of the first and second aspects, reduction in thickness of the information recording apparatus. Moreover, if the housing body is formed from a magnetic plate by a press, a facilitated production process and a reduced cost for a mold can also be achieved.
Additionally, the information recording apparatus may further comprise a carriage axis of magnetic material extending between the cover and the bottom of the housing body for rotatably supporting the carriage. With this arrangement, the carriage axis also provides a path for lines of the magnetic flux connecting the upper and lower yokes in addition to the side yoke, so that the saturation flux density in the yoke may be further improved.
In any aspects of the present invention, the adjustment of the thickness of the cover and housing body may serve to control the density or intensity of the magnetic flux for driving the voice coil. For example, the information recording medium preferably comprises a magnetic disk having a diameter of 1.8 inches or less in case where the present invention is applied to a magnetic disk drive unit including the recording and/or reproducing head comprising a magnetic head.
The magnetic plate employed in the present invention may be a silicon steel plate with nickel plating, a stainless steel plate of SUS4 and SUS3 systems according to Japan Industrial Standard, a vibration suppression plate comprising layers of a synthetic resin material and a metal material, and the like. These plates serve to improve the rigidity of the yoke as compared with yokes of aluminum casting. The improvement of the rigidity in the yoke may contribute to improvement in positioning the head, leading to an accurate writing and/or reading operation of information data. In particular, the employment of the vibration suppression plate serves to prevent vibration from the outside to transmit to the head and/or recording information medium, so that the accurate writing and/or reading operation can be further enhanced.